# Why is density corrected to 15 °C?

> Explains why petroleum density and volume are corrected to the reference temperature of 15 °C, with figures for how much petrol and diesel expand per degree.

Canonical: https://dipdensity.watsinfo.com/guides/why-density-is-corrected-to-15-degree/
Last updated: 2026-11-02

**Short answer:** Fuel expands as it warms, so a warm litre holds less fuel than a cold one and reads lighter on a hydrometer. Correcting density and volume to one reference temperature, 15 °C, lets every reading be compared with every other, whatever the weather.

## Fuel grows when it warms

Every liquid expands with heat, and petrol more than most. Near 745 kg/m³, petrol grows by about **0.12% for each degree**. Diesel near 830 kg/m³ grows by about **0.09%** per degree.

| 10,000 litres at 15 °C becomes | at 25 °C | at 35 °C |
|---|---|---|
| Petrol, 745 kg/m³ | about 10,123 L | about 10,250 L |
| Diesel, 830 kg/m³ | about 10,087 L | about 10,177 L |

The weight stays the same. Only the volume, and so the density, changes.

## Why a reference temperature

Without one, a tanker loaded at a cool depot at dawn and unloaded at a hot pump in the afternoon would show more litres than were loaded, and a lower density. Neither would be real. With every figure corrected to 15 °C, the two ends agree.

15 °C is the reference used across the world's oil trade, and the one ASTM D1250 Tables 53B and 54B are built on.

## In practice

- **Density:** always compare densities at 15 °C. Use [Table 53B](https://dipdensity.watsinfo.com/table-53b/).
- **Volume:** to compare litres at different temperatures, correct them with the [volume correction factor](https://dipdensity.watsinfo.com/tools/volume-correction-factor-calculator/).

## Questions

### How much does petrol expand?

About 0.12% per degree near 745 kg/m³. 10,000 litres of petrol at 15 °C becomes about 10,123 litres at 25 °C.

### Does that mean customers get less fuel in summer?

Dispensers measure litres at the temperature of the fuel. A warm litre holds slightly less fuel by weight than a cold one. That is why depots and large buyers trade at 15 °C, while retail sells by the litre as dispensed.